Tuning pneumatic jetting of metal for additive manufacturing

ABSTRACT

Devices, systems, and methods are directed to adjusting a pneumatic circuit associated with pneumatic ejection of liquid metal from a nozzle as the nozzle moves along a controlled three-dimensional pattern to fabricate a three-dimensional object. The adjustment of the pneumatic circuit can facilitate adjusting a pressure profile within the nozzle as pressurized gas moves through the nozzle to eject, through pneumatic force, liquid metal from the nozzle. Through adjustment of the pneumatic circuit, characteristics of the liquid metal (e.g., size, shape, and flow rate) can be controlled to facilitate control over fabrication of the three-dimensional object.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 §119(e) of U.S. Prov. App.No. 62/303,324, filed on Mar. 3, 2016, the entire contents of which arehereby incorporated herein by reference.

FIELD

The devices, systems, and methods described herein relate to additivemanufacturing, and more specifically to a pneumatic drive system foradditive manufacturing with metallic materials.

BACKGROUND

Pneumatic jetting can be used to drive droplets of metal withpressurized air or gas. Such droplets can be accumulated to form anobject. While pneumatic jetting can impart forces to liquid metal toform a metallic object, considerations related to speed, accuracy,control, and material properties present challenges for the use ofpneumatic forces for object formation on a large scale. Accordingly,there remains a need for commercially viable techniques for additivemanufacturing of metal using pneumatic forces.

SUMMARY

Devices, systems, and methods are directed to the pneumatic ejection ofliquid metal from a nozzle moving along a controlled three-dimensionalpattern to fabricate a three-dimensional object through additivemanufacturing. The metal is movable into the nozzle as a valve isactuated to control movement of pressurized gas into the nozzle. Suchmovement of metal into the valve as pressurized gas is being moved intothe nozzle to create an ejection force on liquid metal in the nozzle canreduce or eliminate the need to replenish a supply of the metal in thenozzle and, therefore can facilitate continuous or substantiallycontinuous liquid metal ejection for the fabrication of parts.

An additive manufacturing system may include a nozzle defining a volumeand a discharge orifice in fluid communication with one another, asource of a pressurized gas, a valve actuatable to control fluidcommunication between the source of pressurized gas and the volume ofthe nozzle, and a media supply in fluid communication with the volume ofthe nozzle. Metal from the media supply may be movable into the volumeof the nozzle as the valve is actuated to eject, under pneumatic forceof the pressurized gas in the nozzle, a liquid form of the metal fromthe discharge orifice along a controlled three-dimensional patternassociated with fabrication of a three-dimensional object.

Implementations may include one or more of the following features. Metalfrom the media supply may be movable into the volume while the valve ispositioned to interrupt fluid communication between the dischargeorifice of the nozzle and the source of the pressurized gas. The nozzlemay further define a first port and a second port, the first port andthe second port spaced apart from one another along the volume of thenozzle, the actuation of the valve controlling movement of thepressurized gas into the volume of the nozzle through the first port.The first port and the second port may be substantially axially alignedwith one another along the volume of the nozzle. The media supply may bein fluid communication with the volume of the nozzle through the secondport. The second port may be vented to the atmosphere. The second portmay be vented to a vacuum. The system may further include a media drainin fluid communication with the volume of the nozzle, where the metalfrom the media supply is movable from the volume of the nozzle to themedia drain. The discharge orifice and the first port may be positionedrelative to one another such that metal moving from the media supply tothe media drain moves between the discharge orifice and the first port.The system may further include a heater arranged to heat at least aportion of the nozzle adjacent to the discharge orifice. The heater maybe one or more of a resistance heater and an induction heater. The metalsupply may be movable into a portion of the volume adjacent to thedischarge orifice. The system may further include an inert gas curtaindisposed at least partially around the discharge orifice.

A method of additive manufacturing may include directing a metal into avolume defined by a nozzle, and moving a discharge orifice and a buildplate relative to one another along a controlled three-dimensionalpattern, where the discharge orifice is defined by the nozzle and influid communication with the volume. The method may also include, basedat least in part on a position of the discharge orifice along thecontrolled three-dimensional pattern, selectively delivering pulses ofpressurized gas into the volume to eject a liquid form of the metal fromthe discharge orifice to form a three-dimensional object on the buildplate, where the metal is directed into the volume defined by the nozzleas the pulses of pressurized gas are selectively delivered into thevolume.

Implementations may include one or more of the following features.Selectively delivering pulses of pressurized gas into the volume toeject the liquid form of the metal may include ejecting the liquid formof the metal from the discharge orifice in a direction having a verticalcomponent opposite a direction of gravity. The method may furtherinclude heating the nozzle at least along a portion of the nozzledefining the discharge orifice. Directing the metal into the volumedefined by the nozzle may include directing a solid form of the metalinto the nozzle. The method may further include venting the pressurizedgas from the volume of the nozzle through a port defined by the nozzleand in fluid communication with the atmosphere or a vacuum. Directingthe metal into the volume may include moving the metal into the volumethrough the port. The pressurized gas may be inert with respect to themetal. The method may further include draining the liquid metal from thevolume of the nozzle as the pulses of pressurized gas are selectivelydelivered into the volume. The liquid form of the metal may be ejectedinto one or more of an inert atmosphere and a vacuum housed within abuild chamber during fabrication of the three-dimensional object. Themethod may further include adjusting the discharge orifice to control ameniscus of the liquid form of the metal at the discharge orifice.

Devices, systems, and methods are directed to adjusting a pneumaticcircuit associated with pneumatic ejection of liquid metal from a nozzleas the nozzle moves along a controlled three-dimensional pattern tofabricate a three-dimensional object. The adjustment of the pneumaticcircuit can facilitate adjusting a pressure profile within the nozzle aspressurized gas moves through the nozzle to eject, through pneumaticforce, liquid metal from the nozzle. Through adjustment of the pneumaticcircuit, characteristics of the liquid metal (e.g., size, shape, andflow rate) can be controlled to facilitate control over fabrication ofthe three-dimensional object.

An additive manufacturing system may include a nozzle defining a volumeand a discharge orifice in fluid communication with one another, thenozzle including an exhaust passage in fluid communication with thevolume. The system may also include a source of a pressurized gas inselective fluid communication with the volume of the nozzle, and a mediasupply in fluid communication with the volume of the nozzle such thatmetal from the media supply is movable into the volume, where theexhaust passage has an adjustable back pressure to control a pressureprofile in the volume of the nozzle as the pressurized gas moves throughthe volume to eject a liquid form of the metal from the dischargeorifice along a controlled three-dimensional pattern for fabrication ofa three-dimensional object.

Implementations may include one or more of the following features. Theexhaust passage may include a hydraulic inductance, the hydraulicinductance having a dissipating resistance to flow in response to forceexerted, over a period of time, on the hydraulic inductance by ventingpressurized gas in the exhaust passage. The hydraulic inductance mayinclude a paddle wheel rotatable in response to force exerted on thepaddle wheel by venting pressurized gas in the exhaust passage. Thepaddle wheel may be rotatable in response to force exerted on the paddlewheel by venting pressurized gas in the exhaust passage. A time-varyingprofile of the resistance of the hydraulic inductance may be adjustable.The exhaust passage may include a variable hydraulic resistance. Thevariable hydraulic resistance may include a variable length of theexhaust passage. The variable hydraulic resistance may include a flowrestriction having a variable size. The system may further include avalve in fluid communication with the source of the pressurized gas andthe volume, where the valve is actuatable to deliver pulses of thepressurized gas to the volume.

A method of additive manufacturing may include directing a metal into avolume defined by a nozzle, the volume in fluid communication with anexhaust passage defined by the nozzle. The method may also includemoving a discharge orifice and a build plate relative to one anotheralong a controlled three-dimensional pattern, the discharge orificedefined by the nozzle and in fluid communication with the volume. Themethod may also include delivering pulses of pressurized gas into thevolume of the nozzle, and adjusting a back pressure of the exhaustpassage through which the pressurized gas is vented from the volume ofthe nozzle, where, in response to the adjustment of the back pressure,the pressurized gas in the volume exerts a force on a liquid form of themetal in the nozzle to eject the liquid metal from the discharge orificeas the discharge orifice and the build plate are moved relative to oneanother along the controlled three-dimensional pattern to form athree-dimensional object on the build plate.

Implementations may include one or more of the following features.Adjusting the back pressure of the exhaust passage may include ventingthe pressurized gas through a hydraulic inductance having a dissipatingresistance to flow in response to force exerted, over a period of time,on the hydraulic inductance by the venting pressurized gas in theexhaust passage. Dissipating resistance may dissipate to a substantiallyconstant hydraulic resistance over the period of time. The period oftime may be less than a period of the pulses of pressurized gasdelivered into the volume of the nozzle. The hydraulic inductance mayinclude a paddle wheel rotatable in response to force exerted on thepaddle wheel by the venting pressurized gas in the exhaust passage.Adjusting the back pressure of the exhaust passage may include ventingthe pressurized gas through a variable hydraulic resistance andadjusting the variable hydraulic resistance based at least in part on aposition of the discharge orifice with respect to the controlledthree-dimensional pattern. The variable hydraulic resistance may includea flow restriction having a variable size and varying the variablehydraulic resistance may include changing the size of the flowrestriction. The variable hydraulic resistance may include a variablelength of the exhaust passage and varying the variable hydraulicresistance may include changing the length of the exhaust passage.Adjusting the back pressure of the exhaust passage may be based on avolume of the liquid form of the metal in the volume of the nozzle. Theexhaust passage may be vented to at least one of atmospheric pressureand a vacuum. The metal may be directed into the volume through theexhaust passage. The method may also include tuning the pulses ofpressurized gas in a multiple of a natural harmonic of the volume of thenozzle.

Devices, systems, and methods are directed to separating sediment fromliquid metal ejected, through pneumatic force, from a nozzle movingalong a controlled three-dimensional pattern to fabricate athree-dimensional object. The separation of the sediment from the liquidmetal can reduce the likelihood that the nozzle will become clogged orotherwise degraded during fabrication of the three-dimensional object orover the course of fabrication of multiple objects. Accordingly, theseparation of the sediment from the liquid metal can facilitate, forexample, the use of pneumatic ejection of liquid metal for high volumeproduction of parts.

An additive manufacturing system may include a nozzle defining a volume,a first port, a second port, and a discharge orifice in fluidcommunication with one another. The system may also include a source ofa pressurized gas in selective fluid communication with the volume ofthe nozzle through the first port, a media supply in fluid communicationwith the volume of the nozzle through the second port, and one or morebaffles disposed in the volume of the nozzle such that an axis definedby the discharge orifice and the second port intersects the one or morebaffles, the one or more baffles oriented to direct sediment of a liquidform of a metal in the volume to a reservoir portion of the volume, thereservoir portion away from the discharge orifice.

Implementations may include one or more of the following features. Theone or more baffles may define a non-linear path between the dischargeorifice and the reservoir portion of the volume. The non-linear pathbetween the discharge orifice and the reservoir portion of the volumemay include an increase in height, along an axis perpendicular to thedischarge orifice, along the non-linear path from the reservoir portionto the discharge orifice. The one or more baffles may span a dimensionof the volume. The one or more baffles may include a plurality ofbaffles substantially parallel to one another. The one or more bafflesmay be angled with respect to an axis perpendicular to the dischargeorifice. The media supply may be configured to move a solid form ofmetal into the volume through the second port. The second port may bevented to atmosphere such that pressurized gas exits the volume throughthe second port. A flow of pressurized gas through the first port may besubstantially unimpeded by the one or more baffles. The system may alsoinclude a heater arranged to heat at least portions of the nozzledefining the discharge orifice and along which the one or more bafflesare disposed. The heater may include one or more of a resistance heater,an induction heater, a convection heater, and a radiation heater.

A method of additive manufacturing may include directing a metal into avolume defined by a nozzle, and moving a discharge orifice and a buildplate relative to one another along a controlled three-dimensionalpattern, where the discharge orifice is defined by the nozzle and influid communication with the volume. The method may also includeseparating, in the volume, a liquid form of the metal from a sediment.Based at least in part on a position of the discharge orifice along thecontrolled three-dimensional pattern, the method may also includedelivering pressurized gas into the volume to eject the liquid form ofthe metal from the discharge orifice to form a three-dimensional objecton the build plate.

Implementations may include one or more of the following features.Separating the liquid form of the metal from the sediment may includemoving the liquid form of the metal along a non-linear path from asediment reservoir in the volume to the discharge orifice. Separatingthe liquid form of the metal from the sediment may further includeincreasing, in the volume, a height of the liquid form of the metalrelative to the discharge orifice. The non-linear path may be at leastpartially defined by one or more baffles disposed in the volume. Theliquid form of the metal may be separated from the sediment as thepressurized gas is delivered into the volume.

Devices, systems, and methods are directed to switching betweenpneumatically actuated ejection and electrically actuated ejection ofliquid metal from a nozzle moving along a controlled three-dimensionalpattern to fabricate a three-dimensional object. Electrically actuatedejection can be useful, for example, for delivering discrete droplets inareas of the object requiring a high degree of accuracy. Pneumaticejection can be useful, for example, for delivering a stream of liquidmetal from the nozzle to provide liquid metal rapidly to areas of theobject that require less accuracy (e.g., an inner portion of theobject). Accordingly, switching between pneumatically actuated ejectionand electrically actuated ejection can facilitate accurate and rapidproduction of parts through additive manufacturing.

A method of additive manufacturing may include directing a metal into avolume defined by a nozzle, and moving a discharge orifice and a buildplate relative to one another along a controlled three-dimensionalpattern, the discharge orifice defined by the nozzle and in fluidcommunication with the volume. The method may also include, based atleast in part on a position of the discharge orifice along thecontrolled three-dimensional pattern, selectively switching betweenpneumatically actuated ejection and electrically actuated ejection of aliquid form of the metal from the discharge orifice. The method may alsoinclude ejecting the liquid form of the metal from the discharge orificeaccording to the selected one of the pneumatically actuated ejection andthe electrically actuated ejection to form at least a portion of athree-dimensional object.

Implementations may include one or more of the following features. Uponselection of the pneumatically actuated ejection, ejecting the liquidform of the metal from the discharge orifice may include ejecting asubstantially constant stream of the liquid form of the metal from thedischarge orifice. Upon selection of the electrically actuated ejection,ejecting the liquid form of the metal from the discharge orifice mayinclude controlling a pulsed electrical current. Droplets of the liquidform of the metal may be ejected from the discharge orifice in responseto the pulsed electrical current. Selectively switching betweenpneumatically actuated ejection and electrically actuated ejection mayinclude selecting the electrically actuated ejection along a border ofthe controlled three-dimensional pattern and selecting the pneumaticallyactuated ejection along an excursion away from the border of thecontrolled three-dimensional pattern. Ejecting liquid metal from thedischarge orifice according to pneumatically actuated ejection mayinclude delivering pressurized air to the volume. The method may furtherinclude venting the pressurized air to one or more of the atmosphere anda vacuum as the liquid form of the metal is ejected through thedischarge orifice. Ejecting liquid metal from the discharge orificeaccording to the electrically actuated ejection may include deliveringan electric current into the liquid form of the metal. The electriccurrent may result in a magnetohydrodynamic force exerted on the liquidform of the metal. The electric current may result in anelectrohydrodynamic force exerted on the liquid form of the metal.Ejecting liquid metal from the discharge orifice according to theelectrically actuated ejection may include delivering an electriccurrent to an actuator in mechanical communication with the liquid formof the metal and movable in response to the electric current to exert amechanical force on the liquid form of the metal to eject the liquidform of the metal from the discharge orifice. The actuator may include apiezoelectric element. The method may further include heating the metalin the volume at least along a portion of the volume defining thedischarge orifice. Directing the metal into the volume may includemoving the metal into the volume as the liquid form of the metal isdischarged from the orifice. The method may further include draining theliquid form of the metal from the volume, through a media drain separatefrom the discharge orifice, as the liquid form of the metal isdischarged from the orifice.

An additive manufacturing system may include a nozzle defining a volumeand a discharge orifice in fluid communication with one another, a buildplate spaced apart from the discharge orifice of the nozzle, a source ofa pressurized gas, an electrical power source, a valve actuatable tocontrol fluid communication between the source of the pressurized gasand the volume of the nozzle, and a robotic system mechanically coupledto the nozzle, where the robotic system is movable to move the dischargeorifice and the build plate relative to one another in three-dimensions.The system may also include a controller in electrical communicationwith the valve, the electrical power source, and the robotic system, thecontroller configured to actuate the robotic system to move thedischarge orifice and the build plate relative to one another along acontrolled three-dimensional pattern, and the controller furtherconfigured to activate the valve and the power source, based at least inpart on a position of the discharge orifice along the controlledthree-dimensional pattern, to selectively switch between pneumaticallyactuated ejection and electrically actuated ejection of a liquid form ofa metal from the discharge orifice to form a three-dimensional object onthe build plate.

Implementations may include one or more of the following features.Selectively switching between pneumatically actuated ejection andelectrically actuated ejection may include selecting the electricallyactuated ejection along a border of the controlled three-dimensionalpattern and selecting the pneumatically actuated ejection along anexcursion away from the border of the controlled three-dimensionalpattern. Upon selection of the pneumatically actuated ejection, thecontroller may actuate the valve to establish fluid communicationbetween the source of the pressurized gas and the volume. Upon selectionof the electrically actuated ejection, the controller may actuate thepower source to deliver electric current to the volume. The controllermay actuate the power source to deliver a pulsed electric current to thevolume.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems and methods described herein are set forth in the appendedclaims. However, for the purpose of explanation, several implementationsare set forth in the following drawings:

FIG. 1 is a block diagram of an additive manufacturing system for usewith pneumatic jetting of metal to form a three-dimensional object.

FIG. 2 shows a flowchart of an exemplary method of additivemanufacturing of metal using pneumatic jetting.

FIG. 3 is a schematic representation of a nozzle including baffles.

FIG. 4 is a flowchart of an exemplary method of separating liquid metalfrom sediment in a pneumatic jetting process for additive manufacturingof metal.

FIG. 5 is a schematic representation of a nozzle including an adjustableexhaust passage.

FIG. 6 is a flowchart of an exemplary method of adjusting back pressurein a pneumatic jetting process for additive manufacturing of metal.

FIG. 7 is a schematic representation of an additive manufacturing systemfor use with pneumatically actuated jetting and electrically actuatedjetting of metal to form a three-dimensional object.

FIG. 8 is a flowchart of an exemplary method of switching betweenpneumatically actuated ejection and electrically actuated ejection ofliquid metal.

DESCRIPTION

Embodiments will now be described with reference to the accompanyingfigures. The foregoing may, however, be embodied in many different formsand should not be construed as limited to the illustrated embodimentsset forth herein.

All documents mentioned herein are hereby incorporated by reference intheir entirety. References to items in the singular should be understoodto include items in the plural, and vice versa, unless explicitly statedotherwise or clear from the text. Grammatical conjunctions are intendedto express any and all disjunctive and conjunctive combinations ofconjoined clauses, sentences, words, and the like, unless otherwisestated or clear from the context. Thus, the term “or” should generallybe understood to mean “and/or” and so forth.

Recitation of ranges of values herein are not intended to be limiting,referring instead individually to any and all values falling within therange, unless otherwise indicated herein, and each separate value withinsuch a range is incorporated into the specification as if it wereindividually recited herein. The words “about,” “approximately,” or thelike, when accompanying a numerical value, are to be construed asindicating a deviation as would be appreciated by one of ordinary skillin the art to operate satisfactorily for an intended purpose. Ranges ofvalues and/or numeric values are provided herein as examples only, anddo not constitute a limitation on the scope of the describedembodiments. The use of any and all examples, or exemplary language(“e.g.,” “such as,” or the like) provided herein, is intended merely tobetter illuminate the embodiments and does not pose a limitation on thescope of the embodiments. No language in the specification should beconstrued as indicating any unclaimed element as essential to thepractice of the embodiments.

In the following description, it is understood that terms such as“first,” “second,” “top,” “bottom,” “up,” “down,” and the like, arewords of convenience and are not to be construed as limiting terms.

Referring now to FIG. 1, a three-dimensional printer 100 can include anozzle 102, a source 104 of pressurized gas, a valve 106, and a mediasupply 108. The nozzle 102 can define a volume 110 and a dischargeorifice 112 in fluid communication with one another. The media supply108 is in fluid communication with the volume 110 of the nozzle 102 and,as described in greater detail below, the media supply 108 moves metal114 into the volume 110 such that a liquid form of the metal 114 isdisposed in the volume 110 along the discharge orifice 112. The valve106 can be actuated to control ejection of the liquid form of the metalfrom the discharge orifice 112. For example, the valve 106 can be movedto an open position to allow pressurized gas to fill the volume 110.Continuing with this example, as the pressurized gas fills the volume110, the pressurized gas exerts a pneumatic force on the liquid form ofthe metal 114 along the discharge orifice 112. This pneumatic force caneject the liquid form of the metal 114 through the discharge orifice112. Additionally, or alternatively, the valve 106 can be moved to aclosed position to interrupt movement of pressurized gas into the volume110 and, thus, interrupt ejection of the liquid form of the metal 114through the discharge orifice 112. Thus, more generally, the valve 106can be selectively actuated to control the ejection of the liquid formof the metal 114 during fabrication of a three-dimensional object 116.

In use, as described in greater detail below, movement of the metal 114into the volume 110 can be separate from actuation of the valve 106,which can facilitate rapidly ejecting the liquid form of the metal 110from the nozzle 102 to form the three-dimensional object 111. Forexample, by reducing or eliminating the need to pause a fabricationprocess to replenish liquid metal in a nozzle, the three-dimensionalprinter 100 can advantageously increase the speed of fabricating thethree-dimensional object 116 through pneumatic jetting of a liquid formof the metal 114. More generally, it should be appreciated that thethree-dimensional printer 100 can be substantially continuously operatedto fabricate one or a plurality of the three-dimensional object 116,making the three-dimensional printer 100 well-suited, for example, toproduce metallic objects at throughput rates suitable for massproduction of parts.

The nozzle 102 can further include a first port 118 and a second port120, each in fluid communication with the volume 110 of the nozzle 102.Pressurized gas from the source 104 of pressurized gas can enter thevolume 110 of the nozzle 102 through first port 118 when the valve 106is open. Additionally, or alternatively, the second port 120 can be influid communication with a lower pressure environment such thatpressurized gas in the volume 110 of the nozzle 102 can exit the nozzle102 through the second port 120. The lower pressure environment can be,for example, at atmospheric pressure. Additionally, or alternatively,the lower pressure environment can be a vacuum, which can facilitateproducing a sharp reduction in pressure once fluid communication betweenthe volume 110 and the source 104 of pressurized gas is interrupted. Incertain implementations, a vacuum pressure can be applied briefly at thesecond port 120, which can be useful for providing further control overthe pressure profile in the volume 110 during ejection of the liquidform of the metal 114 from the discharge orifice 112.

The first port 118 and the second port 120 can be spaced apart from oneanother along the volume 110 of the nozzle 102. For example, the firstport 118 and the second port 120 can be substantially axially alignedwith one another along the volume 110 of the nozzle 102. Such analignment can be useful, for example, for reducing the likelihood ofexciting a resonant frequency in the volume 110 as the pressurized airmoves through the volume 110. In certain instances, the first port 118and the second port 120 can define an axis substantially parallel to aplane containing the discharge orifice 112. In this orientation, thepressurized gas is indirectly directed to the discharge orifice 112,which can advantageously dampen the impact of pressure fluctuations inthe incoming pressurized gas on the ejection of the liquid form of themetal 114.

In some implementations, the discharge orifice 112 can be orientedvertically such that the first port 118 and the second port 120 arebelow the discharge orifice 112. In such instances, the liquid form ofthe metal 114 ejected from the discharge orifice 112 can move in adirection opposite gravity to slow the velocity of the liquid form ofthe metal 114. Such slower velocity can be useful, for example, forachieving an appropriate shape of the metal 114 deposited on thethree-dimensional object 116.

In some implementations, the discharge orifice 112 of the nozzle 102 mayinclude an inert gas curtain around the discharge orifice 112, e.g., inthe form of a ring 113 or other similar structure. This may be usefulwhen operating in atmosphere or similar conditions. Thus, in certainimplementations, an inert gas curtain may be disposed at least partiallyaround the discharge orifice 112.

The discharge orifice 112 of the nozzle 102 may also be modified orotherwise treated to control the liquid form of the metal 114 ejectedfrom the discharge orifice 112. For example, the geometry of thedischarge orifice 112 may be adjustable. In certain aspects, thedischarge orifice 112 may be replaceable or switchable with otherdischarge orifices 112 having different properties, e.g., forcontrolling the liquid form of the metal 114 ejected from the dischargeorifice 112. For example, the discharge orifice 112 may be controlled toprovide an initial condition where the liquid form of the metal 114 hasa meniscus wetting the surface tangent to walls of the discharge orifice112, e.g., by changing the geometry of the discharge orifice 112 orthrough a treatment of the discharge orifice 112. Similarly, thedischarge orifice 112 may be controlled to provide an initial conditionwhere the liquid form of the metal 114 has a meniscus that does not wetthe surface tangent to walls of the discharge orifice 112, e.g., bychanging the geometry of the discharge orifice 112 or through atreatment of the discharge orifice 112.

The source 104 of pressurized gas can be, for example, a pressurizedtank. In certain implementations, the source 104 of the pressurized gascan have a pressure above about 550 kPa. Further, or instead, thepressurized gas can be inert with respect to the liquid form of themetal. For example, in certain instances, the pressurized gas can benitrogen, argon, or air.

As the valve 106 is opened and the pressurized gas initially enters thevolume 110 through the first port 118, pressure in the volume 110initially increases. As described in greater detail below, the pressurein the volume 110 can increase until the pressure in the volume 110 issufficient to overcome a flow resistance associated with the second port120. Upon closing the valve 106, the movement of pressurized gas throughthe first port 118 can be interrupted, and pressure in the volume 110can dissipate as the pressurized gas exits the volume 110 through thesecond port 120.

The metal 114 from the media supply 108 can be movable into the volume110 while the valve 106 is positioned (e.g., closed) to interrupt fluidcommunication between the discharge orifice 112 and the source 104 ofpressurized gas. Thus, for example, the flow rate of the metal from themedia supply 108 into the volume 110 can be decoupled from the flow ofpressurized gas through the volume 110. It should be appreciated thatsuch decoupling can reduce the likelihood that the liquid form of themetal 114 in the volume 110 will become inadvertently depleted as thepressurized gas ejects the liquid form of the metal 114 through thedischarge orifice 112. More generally, movement of the metal 114 fromthe media supply 108 into the volume 110 while the movement ofpressurized gas into the volume 110 is interrupted can reduce thelikelihood of interrupted operation of the nozzle 102 and, thus, canfacilitate continuous or substantially continuous fabrication.

As used herein, the term “metal” shall be understood to include puremetals, metal alloys, and composite materials including one or moremetallic components, unless otherwise specified or made clear by thecontext. Accordingly, by way of non-limiting example, the metal 114 canbe any one or more of aluminum, an aluminum alloy, tin, and solder.

In certain implementations, the media supply 108 can be in fluidcommunication with the volume 110 through the second port 120. Thus, forexample, the metal 114 can be moved (e.g., continuously) by the mediasupply 108 into the volume 110 through the same passage through whichthe pressurized gas is exhausted from the volume 110. It should beappreciated that such a configuration can, for example, reduce thenumber of ports required for the nozzle 102, which can facilitatereducing the size of the nozzle 102, as compared to a nozzle having alarger number of ports.

In some implementations, the nozzle 102 can further include a mediadrain 122 in fluid communication with the volume 110 of the nozzle 102.The metal 114 from the media supply 108 can move from the volume 110 tothe media drain 122 to be drained from the nozzle 102 (e.g., forrecycling to the media supply 108. As an example, the liquid form of themetal 114 moving through the volume 110 of the nozzle 102, from themedia supply 108 to the media drain 122, can move between the dischargeorifice 112 and the first port 118. Accordingly, continuing with thisexample, pressurized gas moving into the volume 110 through the firstport 118 can exert a pneumatic force on the liquid form of the metal 114moving past the discharge orifice 112 to eject the liquid form of themetal 114 through the discharge orifice 112. The movement of the liquidform of the metal 114 from the media supply 108 to the media drain can,for example, reduce the likelihood of sediment build-up in the volume110. It should be appreciated that such a reduction in sediment build-upcan reduce the likelihood of unintended blockage of the dischargeorifice 112 and, thus, can facilitate continuous or substantiallycontinuous ejection of the liquid form of the metal 114 over longperiods of time.

In general, the three-dimensional printer 100 can include a controlsystem 126 that can manage operation of the three-dimensional printer100 to fabricate the three-dimensional object 116. For example, thecontrol system 126 can be in electrical communication with the valve 106and a robotic system 128 mechanically coupled to one or more of thenozzle 102 and a build plate 130. In use, the control system 126 canactuate the robotic system 128 to move the nozzle 102 along a controlledthree-dimensional pattern and additionally, or alternatively, thecontrol system 126 can actuate the valve 106 to control ejection of aliquid form of the metal 114 from the nozzle 102 as one or more of thenozzle 102 and the build plate 130 are moved along the controlledthree-dimensional pattern. The controlled three-dimensional pattern canbe based on a three-dimensional model 134 stored, for example, in adatabase 132, such as a local memory of a computer used as the controlsystem 126, or a remote database accessible through a server or otherremote resource, or in any other computer-readable medium accessible tothe control system 126. In certain implementations, the control system126 can retrieve the three-dimensional model 134 in response to userinput, and generate machine-ready instructions for execution by thethree-dimensional printer 100 to fabricate the three-dimensional object116.

The robotic system 128 can be movable within a working volume 136 of abuild chamber 138 to position the nozzle 102 and the build plate 130relative to one another in the build chamber 138 along the controlledthree-dimensional pattern to fabricate the three-dimensional object 116.A variety of robotics systems are known in the art and suitable for useas the robotic system 128 contemplated herein. For example, the roboticsystem 128 can include a Cartesian or x-y-z robotics system employing anumber of linear controls to move independently in the x-axis, they-axis, and the z-axis within the build chamber 138. Additionally, oralternatively, the robotic system 128 can include delta robots, whichcan, in certain implementations, provide significant advantages in termsof speed and stiffness, as well as offering the design convenience offixed motors or drive elements. Other configurations such as double ortriple delta robots can, additionally or alternatively, be used and canincrease range of motion using multiple linkages. More generally, anyrobotics suitable for controlled positioning of the nozzle 102 and thebuild plate 130 relative to one another, especially within a vacuum orsimilar environment, may form part of the robotic system 114, includingany mechanism or combination of mechanisms suitable for actuation,manipulation, locomotion and the like within the build chamber 138.

The build chamber 138 may include a relatively inert atmosphere. Thebuild chamber 138 may also or instead include a vacuum. In this manner,the liquid form of the metal 114 may be ejected into one or more of aninert atmosphere and a vacuum during fabrication of a three-dimensionalobject 116.

The media supply 108 can include, for example, a drive chain 140 and aheater 142. In certain implementations, the metal 114 is initially in asolid form, such as, for example, a continuous form (e.g., wire) or adiscrete form (e.g., a billet). For example, the metal 114 can besupplied in discrete units one-by-one as billets or the like into theheater 126. Additionally, or alternatively, the metal 114 can besupplied from a spool or cartridge containing the metal 114 in a wireform. For environmentally sensitive materials, the media supply 108, thebuild chamber 138, or both, can provide a vacuum environment for themetal 114. More generally, one or more of the media supply 108 and thebuild chamber 120 can maintain a suitably inert environment for handlingof the metal 114, such as a vacuum, and oxygen-depleted environment, aninert gas environment, or some gas or combination of gasses that are notreactive with the metal 114 under the conditions maintained duringthree-dimensional fabrication.

In implementations in which the metal is initially in a solid form, thedrive chain 140 can engage the metal and move the metal into the heater142, where a liquid form of the metal can be formed. The heater 142 canbe in fluid communication with the nozzle 102 such that the liquid formof the metal is movable into the nozzle as fluid communication betweenthe pressurized gas and the nozzle 102 is, for example, separatelycontrolled by actuation of the valve 106. While the media supply 108 isdescribed as including a solid form of the metal 110 initially, itshould be appreciated that, in some implementations, the metal 116 caninitially be in a liquid form without departing from the scope of thepresent disclosure. In such implementations, the media supply 108 may,for example, feed a liquid form of the metal 116 into the nozzle 102through the force of gravity, through the use of a pump, or acombination thereof.

The drive chain 140 can include, for example, any suitable gears,compression pistons, or the like, for continuous or indexed feeding ofthe metal 110 into the heater 142. In one aspect, the drive chain 140can include a plurality of rollers 144 between which a solid form of themetal 114 can be pinched such that rotation of the plurality of rollerscan move the solid form of the metal 114 into the heater 142.

The heater 142 can heat the solid form of the metal 114 beyond a melttemperature of the metal 114 to form a liquid form of the metal 114. Anynumber of heating techniques may be used. In one aspect, electricaltechniques such as inductive or resistive heating may be usefullyapplied to liquefy the metal 114. This can include, for example,inductively or resistively heating a chamber around the metal 114.Additionally, or alternatively, the heater 142 can include one or moreof induction heating and radiative heating to liquefy the metal 114.

While the heater 142 is shown as being outside of the nozzle 102, itshould be appreciated, that the heater 142 can be, additionally oralternatively, integrated into the nozzle 102 such that, for example, asolid form of the metal 110 is moved from the metal supply into thenozzle 102 and the solid form of the metal 110 is melted as it passesinto the nozzle 102. In such implementations, the heater 142 can, forexample, direct heat in the vicinity of the discharge orifice 112. Ingeneral, direction of heat in the vicinity of the discharge orifice 112can reduce the likelihood of solidification of the liquid form of themetal 114 in the discharge orifice 112 and, thus, can reduce thelikelihood of the nozzle 102 seizing or otherwise becoming inoperableduring a fabrication process. For example, the heater 142 can reduce thelikelihood of solidification of the liquid form of the metal 114 in ornear the discharge orifice 112 during a quiescent state in which theliquid form of the metal 114 is not being ejected from the dischargeorifice 112 (e.g., between part fabrications).

The heater 142 can also or instead include any other heating systemssuitable for applying heat to the metal 110 to a suitable temperaturefor producing or maintaining a liquid form of the metal 110. Thus, theheater 106 described herein should be understood to include generallyany system that places a solid form of the metal 110 in condition foruse in fabrication as contemplated herein and further includes anysystem that maintains a liquid form of the metal 114 in condition foruse in fabrication as contemplated herein. In certain implementations,the system 100 can further include a heater 124 disposed along a portionof the nozzle 102 adjacent (e.g., directly adjacent) to the dischargeorifice 112.

FIG. 2 shows a flowchart of an exemplary method 200 of additivemanufacturing of metal using pneumatic jetting. The method 200 can becarried out using any one or more of the devices and systems describedherein, unless otherwise specified or made clear from the context. Thus,for example, it should be understood that the method 200 can be carriedout using the three-dimensional printer 100 described above with respectto FIG. 1.

As shown in step 202, the method 200 may include directing a metal intoa volume defined by the nozzle. For example, a solid form of the metalcan be directed into the volume defined by the nozzle. In certainimplementations, the solid form of the metal can be liquefied within thevolume defined by the nozzle. Additionally, or alternatively, the metalcan be liquefied outside of the volume defined by the nozzle anddelivered into the volume in a liquid form.

As shown in step 204, the method 200 can include moving a dischargeorifice and a build plate relative to one another along a controlledthree-dimensional pattern. Such relative movement can be achieved in oneor more of various different combinations of movement of the dischargeorifice and the build plate. For example, the discharge orifice can bemoved along the controlled three-dimensional pattern while the buildplate remains stationary. Additionally, or alternatively, the buildplate can be moved along the controlled three-dimensional pattern whilethe discharge orifice remains stationary. Further or instead, thedischarge orifice and the build plate can each be moved along thecontrolled three-dimensional pattern.

The discharge orifice can be defined by the nozzle and in fluidcommunication with the volume such that the liquid form of the metal canmove from the volume through the discharge orifice as the dischargeorifice and the build plate are moved relative to one another along thecontrolled three-dimensional pattern. In certain implementations, arobotic system can move the discharge orifice and the build platerelative to one another along the controlled three-dimensional pattern.The robotic system can be, for example, any one or more of the variousdifferent robotic systems described herein or otherwise known in theart. Additionally, or alternatively, actuation of the robotic system tomove the discharge orifice and the build plate relative to one anothercan be controlled by a control system, such as any one or more of thevarious control systems described herein. For example, the controlsystem can control actuation of the robotic system based at least inpart upon a three-dimensional model received by the control system.

As shown in step 206, the method 200 can include selectively deliveringpulses of pressurized gas into the volume to eject a liquid form of themetal from the discharge orifice to form a three-dimensional object. Theselective delivery of the pulses can be, for example, based at least inpart on a position of the discharge orifice along the controlledthree-dimensional pattern. In certain implementations, the metal can bedirected into the volume according to step 202 while the pulses ofpressurized gas are selectively delivered into the volume. In someimplementations, the metal in the liquid form can be drained from thevolume of the nozzle as the pulses of pressurized gas are selectivelydelivered into the volume. Thus, more generally, the metal can be movedin and out of the volume of the nozzle independently of delivery of thepressurized gas into the volume of the nozzle.

Further, or instead, selectively delivering pulses of pressurized gasinto the volume to eject the liquid form of the metal can includeejecting the liquid form of the metal from the discharge orifice in adirection having a vertical component substantially opposite a directionof gravity. It should be understood that the ejection of the liquid formof the metal in this direction can advantageously slow down the ejectedliquid form of the metal to achieve desired contact between the ejectedliquid form of the metal and a three-dimensional object beingfabricated.

In certain implementations, selectively delivering pulses of pressurizedgas into the volume to eject the liquid form of the metal can includecontrolling the pulse frequency. The pulse frequency may be controlledor tuned to increase a stability of a meniscus of the liquid metal priorto droplet ejection, e.g., between each ejection. In certain aspects,the pulse frequency may be tuned in multiples of the natural harmonicsof the volume of the nozzle.

While certain implementations have been described, other implementationsare additionally, or alternatively, possible.

For example, while nozzles have been described as having an unimpededpath between metal entering the nozzle and a discharge orifice throughwhich metal is ejected from the nozzle, other configurations areadditionally or alternatively possible. As an example, referring now toFIG. 3, a nozzle 300 can define a volume 302, a first port 304, a secondport 306, and a discharge orifice 308 in fluid communication with oneanother. In general, unless otherwise specified or made clear from thecontext, the nozzle 300 can be used in addition to or in place of thenozzle 102 of the three-dimensional printer 100 described above withrespect to FIG. 1. Thus, for example, the nozzle 300 can be in selectivefluid communication with pressurized gas from a source of pressurizedgas, such as the source 104 of the pressurized gas described above withrespect to FIG. 1, with the fluid communication with the volume 302being through the first port 304. Similarly, the nozzle 300 can receivemetal from a media supply, such as the media supply 108 described abovewith respect to FIG. 1, in fluid communication with the volume 302 ofthe nozzle through the second port 306. Thus, for example, it should beunderstood that the nozzle 300 can receive a solid form of metal throughthe second port 306 and, additionally or alternatively, the second port306 can be vented to one or both of an atmospheric pressure and a vacuumpressure such that pressurized gas can exit the volume through thesecond port 306.

The nozzle 300 can include one or more baffles 310 disposed in thevolume 302 (e.g., a plurality of baffles 310 arranged substantiallyparallel to one another). In general, the baffles 310 can be oriented todirect sediment toward a reservoir portion 312 of the volume 302. Thereservoir portion 312 can be away from the discharge orifice 308 of thenozzle 300 such that sediment directed toward the reservoir portion 312remains away from the discharge orifice 308 as the liquid metal isejected from the discharge orifice 308 during use of the nozzle 300.

In certain implementations, an axis defined by the discharge orifice 308and the second port 306 intersects the one or more baffles 310. In suchimplementations, the flow of metal moving into the volume 302 throughthe second port 306 will be disturbed by the one or more baffles 310 asthe metal moves toward the discharge orifice 308. It should beappreciated that such disturbance of the flow of the metal can be usefulfor directing sediment toward the reservoir portion 312 of the volume302. Further, or instead, the one or more baffles 310 can be angled, forexample, with respect to an axis perpendicular to the discharge orifice308 to direct sediment, for example, toward the reservoir portion 312 ofthe volume 302.

In some implementations, the one or more baffles 310 can span adimension of the volume 302 of the nozzle 300. For example, the one ormore baffles 310 can span a depth of the volume 302 and span less thanthe entirety of the width of the volume 302. In general, spanning adimension of the volume 302 with the one or more baffles 310 canincrease the likelihood that the flow of the liquid metal from thesecond port 306 toward the discharge orifice 308 will be directed to thereservoir portion 312 before reaching the discharge orifice 308.

In addition, or in the alternative, the one or more baffles 310 candefine a non-linear path between the discharge orifice 308 and thereservoir portion 312. As an example, the non-linear path can include asection increasing in height, along an axis perpendicular to thedischarge orifice 308 such that liquid metal moving from the reservoirportion 312 toward the discharge orifice 308 follows the increase inheight. Such an increase in height can be useful for separating sedimentfrom the liquid metal before the liquid metal reaches the dischargeorifice. More generally, a non-linear path can be useful, for example,for reducing the likelihood that sediment will migrate from thereservoir portion 312 to the discharge orifice 308 during sustained useof the nozzle 300 to eject a liquid form of a metal.

In general, pressurized gas can be moved through the volume 302, fromthe first port 304 to the second port 306, in any one or more of variousdifferent directions. It should be appreciated, however, that certainorientations of the first port 304 and the second port 306 can beadvantageous for efficient and accurate operation of the nozzle 300 toeject liquid metal. Thus, in certain implementations, the flow ofpressurized gas through the first port 304 can be substantiallyunimpeded by the one or more baffles 310 such that the one or morebaffles 310 do not slow down the movement of pressurized gas into thevolume 300 during use.

The nozzle 300 can, in some implementations, include a heater 314. Theheater 314 can, for example, direct heat along at least portions of thenozzle 300 defining the discharge orifice 308 and along which the one ormore baffles 310 are disposed. The application of heat along suchportions of the nozzle 300 can reduce the likelihood that the liquidmetal will solidify as the liquid metal is moving along the one or morebaffles 310 and toward the discharge orifice 308. The heater 314 caninclude, for example, one or more of a resistance heater, an inductionheater, a convection heater, and a radiation heater.

FIG. 4 is a flowchart of an exemplary method 400 of separating liquidmetal from sediment in a pneumatic jetting process for additivemanufacturing of metal. The method 400 can be carried out using any oneor more of the three-dimensional printers described herein, unlessotherwise specified or made clear from the context. Thus, for example,the method 400 can be carried out using a three-dimensional printer,such as the three-dimensional printer 100 described above with respectto FIG. 1, including the nozzle 300 described above with respect to FIG.3.

As shown in step 402, the method 400 can include directing a metal intoa volume defined by a nozzle. In general, the metal can be directed intothe volume according to any one or more of the methods described herein.Thus, for example, a solid form of the metal can be directed into thevolume defined by the nozzle such that the solid form of the metal canbe liquefied within the volume defined by the nozzle. Additionally, oralternatively, the metal can be liquefied outside of the volume definedby the nozzle and delivered into the volume in a liquid form.

As shown in step 404, the method 400 can include moving a dischargeorifice and a build plate relative to one another along a controlledthree-dimensional pattern. The discharge orifice can be defined by thenozzle and in fluid communication with the volume such that metal in thevolume can move through the discharge orifice along the controlledthree-dimensional pattern. It should be appreciated that the relativemovement of the discharge orifice and the build plate can be achieved bymoving one or both of the discharge orifice and the build plate relativeto one another.

As shown in step 406, the method 400 can include separating a liquidform of the metal from a sediment. The separation can take place, forexample, in the volume defined by the nozzle, and the volume can definea sediment reservoir. The separation can include, for example, movingthe liquid form of the metal along a non-linear path from the sedimentreservoir to the discharge orifice (e.g., a non-linear path at leastpartially defined by baffles disposed in the volume defined by thenozzle). The movement of the liquid form of the metal along thenon-linear path can facilitate, for example, separation of the liquidform of the metal from the sediment. Additionally, or alternatively,separating the liquid form of the metal from the sediment can includeincreasing, in the volume of the nozzle, a height of the liquid form ofthe metal relative to the discharge orifice. As the height of the liquidform of the metal increases, the sediment will settle and, thus,separate from the liquid form of the metal.

As shown in step 408, the method 400 can include delivering pressurizedgas into the volume to eject the liquid form of the metal from thedischarge orifice to form a three-dimensional object. The delivery ofthe pressurized gas can be, for example, based at least in part on aposition of the discharge orifice along the controlled three-dimensionalpattern such that the ejected metal can be accurately delivered to thethree-dimensional object being fabricated. Additionally, oralternatively, the separation of the liquid form of the metal from thesediment in step 406 can occur while the pressurized gas is deliveredinto the volume such that the separation of the liquid metal from thesediment does not significantly impact the speed of fabrication of thethree-dimensional object.

As another example, while nozzles have been described as having a fixedpressure profile, other implementations are additionally oralternatively possible. As an example, referring now to FIG. 5, a nozzle500 can define a volume 502, a first port 504, a second port 506, and adischarge orifice 508 in fluid communication with one another. Further,or instead, the nozzle 500 can include an exhaust passage 510, asdescribed in greater detail below. In general, unless otherwisespecified or made clear from the context, the nozzle 500 can be used inaddition to or in place of the nozzle 102 of the three-dimensionalprinter 100 described above with respect to FIG. 1 or the nozzle 300described above with respect to FIG. 3. Thus, for example, the nozzle500 can be in selective fluid communication with pressurized gas from asource of pressurized gas, such as the source 104 of the pressurized gasdescribed above with respect to FIG. 1, with the fluid communicationwith the volume 502 being through the first port 504. Similarly, thenozzle 500 can receive metal from a media supply, such as the medialsupply 108 described above with respect to FIG. 1, which can be in fluidcommunication with the volume 502 through the second port 306. Thus, forexample, it should be understood that the nozzle 300 can receive a solidform of metal through the second port 506 and, additionally oralternatively, the second port 506 can be vented through the exhaustpassage 510.

The exhaust passage 510 can have an adjustable back pressure. Ingeneral, such adjustable back pressure can be useful for controlling apressure profile in the volume 502 defined by the nozzle 500 aspressurized gas moves through the volume 502 to eject a liquid form ofthe metal from the discharge orifice 508 (e.g., along a controlledthree-dimensional pattern for fabrication of a three-dimensionalobject). As used herein, the pressure profile in the volume 502 includespressure in the volume 502 as a function of time. It should beappreciated that characteristics of the pressure profile (e.g., rate ofpressure rise, peak pressure, rate of pressure decay, and duration) canimpact the shape of droplets ejected from the discharge orifice 508 inresponse to pulsations of the pressurized gas in the nozzle 500.

In certain implementations, the exhaust passage 510 can include ahydraulic inductance 512. As pressurized gas moves through the hydraulicinductance 512, the hydraulic inductance 512 can have a dissipatingresistance, over time, in response to force exerted on the hydraulicinductance 512 as the pressurized gas exits the volume 502 through theexhaust passage 510. For example, as pressurized gas is initiallyintroduced to the hydraulic inductance 512, the flow resistance of thehydraulic inductance 512 can be high such that pressure builds in thevolume 502. Continuing with this example, as the pressurized gascontinues to exert force on the hydraulic inductance 512, the flowresistance of the hydraulic inductance 512 can decrease such that thebuilt-up pressure in the volume 502 can dissipate as the pressurized gasmoves through the hydraulic inductance 512 at a higher rate.

As an example, the hydraulic inductance 512 can include a paddle wheel514. In use, the paddle wheel 514 can rotate in response to forceexerted on the paddle wheel 514 by the venting pressurized gas in theexhaust passage 510. The paddle wheel 514 can have an inertia that mustbe overcome before the paddle wheel 514 can rotate freely. It should beappreciated that the force of the pressurized gas on the paddle wheel514 prior to overcoming the inertia can correspond to a rise in pressurein the volume 502. As the pressurized gas continues to be exerted on thepaddle wheel 514 and the inertia is overcome, the paddle wheel 514 canrotate freely such that the paddle wheel 514 exerts little to knowresistance on the flow of the pressurized gas.

In certain implementations, the time-varying profile of the resistanceof the hydraulic inductance 512 can be adjustable to facilitateachieving a desired pressure profile (e.g., in real-time) in the volume502. Such adjustability can be useful, for example, for controlling thesize and shape of droplets ejected from the discharge orifice 508. Forexample, in implementations in which the hydraulic inductance 512includes the paddle wheel 514, a rotational resistance of the paddlewheel 514 can be adjusted to change the time-varying profile of theresistance of the hydraulic inductance 512.

In certain implementations, the exhaust passage 510 can include avariable hydraulic resistance 516. As an example, the variable hydraulicresistance 516 can include a variable length of the exhaust passage 510,with longer lengths generally corresponding to increased hydraulicresistance. Additionally, or alternatively, the variable hydraulicresistance 516 can include a flow restriction (e.g., an orifice) havinga variable size. In certain implementations, the variable hydraulicresistance 516 can be adjusted to achieve a target pressure profile(e.g., in real-time) in the volume 502.

FIG. 6 is a flowchart of an exemplary method 600 of adjusting backpressure in a pneumatic jetting process for additive manufacturing ofmetal. The method 600 can be carried out using any one or more of thethree-dimensional printers described herein, unless otherwise specifiedor made clear from the context. Thus, for example, the method 600 can becarried out using a three-dimensional printer, such as thethree-dimensional printer 100 described above with respect to FIG. 1,including the nozzle 500 described above with respect to FIG. 5.

As shown in step 602, the method 600 can include directing a metal intoa volume defined by the nozzle. In general, the metal can be directedinto the volume according to any one or more of the methods describedherein. Thus, for example, a solid form of the metal can be directedinto the volume defined by the nozzle such that the solid form of themetal can be liquefied within the volume defined by the nozzle.Additionally, or alternatively, the metal can be liquefied outside ofthe volume defined by the nozzle and delivered into the volume in aliquid form.

As shown in step 604, the method 600 can include moving a dischargeorifice and a build plate relative to one another along a controlledthree-dimensional pattern. The discharge orifice can be defined by thenozzle and in fluid communication with the volume such that a liquidform of the metal can be ejected through the discharge orifice as thedischarge orifice and the build plate are moved relative to one anotheralong the controlled three-dimensional pattern.

As shown in step 606, the method 600 can include delivering pulses ofpressurized gas into the volume of the nozzle. For example, deliveringpulses of pressurized gas can include repeatedly actuating a valvedisposed between the volume and a source of the pressurized gasaccording to any one or more of the various different methods describedherein. It should be appreciated that, in general, the characteristicsof the pulsations (e.g., amplitude and rate) can be a function of theshape and size of liquid metal droplets desired for a given positionalong the controlled three-dimensional pattern.

As shown in step 608, the method 600 can include adjusting a backpressure of an exhaust passage in fluid communication with the volume ofthe nozzle and through which the pressurized gas is vented from thevolume of the nozzle. In general, in response to the adjustment of theback pressure, the pressurized gas in the volume can exert a force(e.g., a changing force) on the liquid form of the metal in the volumeto eject the liquid metal from the discharge orifice. As the dischargeorifice and the build plate are moved relative to one another along thecontrolled three-dimensional pattern, the ejected liquid metal canaccumulate to form a three-dimensional object on the build plate.

Adjusting the back pressure in step 608 can include any one or more ofthe adjustments described above with respect to the nozzle 500 of FIG.5. As an example, adjusting the back pressure in step 608 can includeventing the pressurized gas through a hydraulic inductance having adissipating resistance to flow in response to force exerted by theventing pressurized gas. In general, the hydraulic inductance can be anyof the various different hydraulic inductances described herein and,therefore, can include a paddle wheel (e.g., the paddle wheel 514 ofFIG. 1) or other similar devices. The dissipating resistance can have aprofile suited to achieving a desired pressure profile in the volume asthe pressurized gas is pulsed in the volume. In certain implementations,the dissipating resistance can dissipate to a substantially constanthydraulic resistance in the exhaust passage. Additionally, oralternatively, the period of time over which the resistance dissipatescan be less than a period of the pulses of the pressurized gas in thevolume. Such a rapid dissipation can be useful, for example, forcontrolling the size and shape of the ejected liquid metal.

As an additional, or alternative, example, adjusting the back pressurein step 608 can include venting the pressurized gas through a variablehydraulic resistance and adjusting the variable hydraulic resistance.For example, the hydraulic resistance can be varied based at least inpart on a position of the discharge orifice with respect to thecontrolled three-dimensional pattern. It should be appreciated thatvarying hydraulic resistance can include any one or more of the methodsof varying hydraulic resistance described herein and, therefore, caninclude one or more of varying size of a flow restriction and varying alength of an exhaust passage.

In certain implementations, adjusting the back pressure of the exhaustpassage in step 608 can be based on a volume of the liquid form of themetal in the volume of the nozzle. As an example, the back pressure canbe adjusted to a higher pressure as the volume of the liquid form of themetal in the volume of the nozzle increases. The higher back pressurecan correspond to a higher pressure in the volume. In turn, the increasein back pressure can increase the amount of the liquid form of the metalejected from the discharge orifice and, thus, reduce the volume of theliquid form of the metal in the volume of the nozzle. It should beappreciated that a reduction in the back pressure can decrease theamount of the liquid form of the metal ejected from the dischargeorifice and, thus, increase the volume of the liquid form of the metalin the volume of the nozzle.

As another example, while additive manufacturing systems have beendescribed as including pneumatic jetting, other configurations areadditionally or alternatively possible. For example, referring now toFIG. 7, a three-dimensional printer 700 switchable between pneumaticallyactuated ejection and electrically actuated ejection. Unless otherwisespecified or made clear by the context, elements having “700” serieselement numbers are the same as elements having analogous “100” serieselement numbers in FIG. 1. Thus, for example, the robotic system 708 inFIG. 7 should be understood to be analogous to the robotic system 108 inFIG. 1, unless otherwise specified or made clear from the context.Accordingly, for the sake of efficient explanation, elements having“700” series element numbers are not described separately from theanalogous elements having “100” series element numbers, except to pointout features related to switching between pneumatically actuatedejection and electrically actuated ejection. As used herein,“pneumatically actuated ejection” should be understood to includeejection of liquid metal through the application of a pneumatic forceexerted, directly or indirectly, on the liquid metal through the forceof a pressurized gas. Also, as used herein, “electrically actuatedejection” should be understood to include ejection of liquid metalthrough the application of a magnetohydrodynamic force, anelectrohydrodynamic force, or an electro-mechanically actuated force onthe liquid metal.

The three-dimensional printer 700 can include a control system 726 inelectrical communication with a valve 706 and an electrical power source709. The valve 706 can be actuatable to control fluid communicationbetween a source 704 of pressurized gas and a volume 710 defined by anozzle 702, as described above with respect to the valve 106 in FIG. 1.electrical communication with the nozzle 702 and the control system 726.In use, the control system 726 can control the valve 706 and theelectrical power source 709 to selectively switch between pneumaticallyactuated ejection and electrically actuated ejection of a liquid form ofa metal 714 from a discharge orifice 712 defined by the nozzle 702.

In certain implementations, the control system 726 can place the nozzle702 in a pneumatically actuated ejection mode by actuating the valve 706to establish fluid communication between the source 704 of pressurizedgas and the volume 710 defined by the nozzle 702 to eject a liquid formof the metal 714 according to any one or more of the methods describedherein. In the pneumatically actuated ejection mode, the control system726 can, optionally, interrupt electrical communication between theelectrical power source 709 and the nozzle 702.

Further, or instead, the control system 726 can place the nozzle 702 inan electrically actuated ejection mode by actuating the valve 706 tointerrupt fluid communication between the source 704 of pressurized gasand the volume 710 and actuating the electrical power source 709 todeliver electric current to the nozzle 702. It should be appreciatedthat the electric current can be, for example, a pulsed electric currentto eject discrete liquid metal droplets (e.g., drop-on-demand) from thedischarge orifice 712. In certain implementations, the electric currentcan be directed into the liquid form of the metal in the nozzle 702,where the electric current can intersect a magnetic field extendingthrough the liquid form of the metal to create a magnetohydrodynamicforce to eject the liquid form of the metal 714 from the dischargeorifice 712. In some implementations, the electric current can bedirected into the liquid form of the metal in the nozzle 702, where theelectric current can interact with an electric charge of the liquid formof the metal 714 to create an electrohydrodynamic force to eject theliquid form of the metal 714 from the discharge orifice 712.Additionally, or alternatively, the electric current can be directed toan actuator 727 (e.g., a piezoelectric actuator) in contact with theliquid form of the metal 714 such that actuation of the actuator 727exerts a mechanical force on the liquid form of the metal 714 toejection the liquid form of the metal 714 from the discharge orifice712.

In some implementations, the control system 726 can actuate the valve706 and the electrical power source 709 to switch between pneumaticallyactuated ejection and electrically actuated ejection based at least inpart on a position of the discharge orifice 712 along a controlledthree-dimensional patter. As an example, the control system 726 canactuate the valve 706 and the electrical power source 709 forelectrically actuated ejection along a border of the controlledthree-dimensional pattern or another similar region requiring a highdegree of accuracy of placement of liquid metal droplets. As anadditional or alternative example, the control system 726 can actuatethe valve 706 and the electrical power source 709 for pneumaticallyactuated ejection along an excursion away from the border (e.g., withinan interior space defined by the border) of the controlledthree-dimensional pattern or along another similar region requiring lessaccuracy in placement of liquid metal. More generally, the controlsystem 726 can actuate the valve 706 and the electrical power source toswitch between ejection of a stream of the liquid form of the metal 714(in the pneumatically actuated ejection mode) and ejection of discretedroplets of the liquid form of the metal 714 (in the electricallyactuated ejection mode).

FIG. 8 is a flowchart of an exemplary method 800 of switching betweenpneumatically actuated jetting and electrically actuated jetting of aliquid form of a metal. It should be appreciated that the exemplarymethod 800 can be carried out using, for example, the three-dimensionalprinter 700 described above with respect to FIG. 7.

As shown in step 802, the exemplary method 800 can include directing ametal into a volume defined by nozzle. In general, the metal can bedirected into the volume according to any one or more of the methodsdescribed herein and, thus, can include movement of the metal throughthe use of any one or more of the media supplies described herein.

As shown in step 804, the exemplary method 800 can include moving adischarge orifice and a build plate relative to one another along acontrolled three-dimensional pattern. The discharge orifice can any oneor more of the discharge orifices described herein and, thus, can bedefined by the nozzle and in fluid communication with the volume. Thedischarge orifice and the build plate can be moved relative to oneanother through the use of a robotic system, such as the robotic systems108 and 708 described above.

As shown in step 806, the exemplary method 800 can include selectivelyswitching between pneumatically actuated ejection and electricallyactuated ejection of a liquid form of the metal from the dischargeorifice. The selective switching can be, for example, based at leastupon a position of the discharge orifice along the controlledthree-dimensional pattern. As an example, the selective switching caninclude selecting electrically actuated ejection along a border of thecontrolled three-dimensional pattern (e.g., to deliver discrete dropletsalong the border, where more accuracy may be required to be meet partspecifications). Additionally, or alternatively, the selective switchingcan include selecting pneumatically actuated ejection along an excursionaway from the border of the controlled three-dimensional pattern. Suchpneumatic ejection can be useful, for example, within the border, whereaccurate placement of the liquid metal may be less critical. Thus, forexample, in such regions within the border, the pneumatic ejection candeliver a constant or substantially constant stream of liquid metal toin-fill the part and, thus, speed up the manufacturing process.

As shown in step 808, the exemplary method 800 can include ejecting theliquid metal from the discharge orifice according to the selected one ofthe pneumatically actuated ejection and the electrically actuatedejection to form at least a portion of a three-dimensional object.

The above systems, devices, methods, processes, and the like may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. This includes realization inone or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors or otherprogrammable devices or processing circuitry, along with internal and/orexternal memory. This may also, or instead, include one or moreapplication specific integrated circuits, programmable gate arrays,programmable array logic components, or any other device or devices thatmay be configured to process electronic signals. It will further beappreciated that a realization of the processes or devices describedabove may include computer-executable code created using a structuredprogramming language such as C, an object oriented programming languagesuch as C++, or any other high-level or low-level programming language(including assembly languages, hardware description languages, anddatabase programming languages and technologies) that may be stored,compiled or interpreted to run on one of the above devices, as well asheterogeneous combinations of processors, processor architectures, orcombinations of different hardware and software. In another aspect, themethods may be embodied in systems that perform the steps thereof, andmay be distributed across devices in a number of ways. At the same time,processing may be distributed across devices such as the various systemsdescribed above, or all of the functionality may be integrated into adedicated, standalone device or other hardware. In another aspect, meansfor performing the steps associated with the processes described abovemay include any of the hardware and/or software described above. Allsuch permutations and combinations are intended to fall within the scopeof the present disclosure.

Embodiments disclosed herein may include computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps thereof. The code may be stored in a non-transitory fashion ina computer memory, which may be a memory from which the program executes(such as random access memory associated with a processor), or a storagedevice such as a disk drive, flash memory or any other optical,electromagnetic, magnetic, infrared or other device or combination ofdevices. In another aspect, any of the systems and methods describedabove may be embodied in any suitable transmission or propagation mediumcarrying computer-executable code and/or any inputs or outputs fromsame.

The method steps of the implementations described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So, for example performing the step of X includes anysuitable method for causing another party such as a remote user, aremote processing resource (e.g., a server or cloud computer) or amachine to perform the step of X. Similarly, performing steps X, Y and Zmay include any method of directing or controlling any combination ofsuch other individuals or resources to perform steps X, Y and Z toobtain the benefit of such steps. Thus, method steps of theimplementations described herein are intended to include any suitablemethod of causing one or more other parties or entities to perform thesteps, consistent with the patentability of the following claims, unlessa different meaning is expressly provided or otherwise clear from thecontext. Such parties or entities need not be under the direction orcontrol of any other party or entity, and need not be located within aparticular jurisdiction.

It should further be appreciated that the methods above are provided byway of example and not limitation. Absent an explicit indication to thecontrary, the disclosed steps may be modified, supplemented, omitted,and/or re-ordered without departing from the scope of this disclosure.Numerous variations, additions, omissions, and other modifications willbe apparent to one of ordinary skill in the art. In addition, the orderor presentation of method steps in the description and drawings above isnot intended to require this order of performing the recited stepsunless a particular order is expressly required or otherwise clear fromthe context. Thus, while particular embodiments have been shown anddescribed, it will be apparent to those skilled in the art that variouschanges and modifications in form and details may be made thereinwithout departing from the spirit and scope of this disclosure and areintended to form a part of the invention as defined by the followingclaims, which are to be interpreted in the broadest sense allowable bylaw.

What is claimed is:
 1. An additive manufacturing system, the systemcomprising: a nozzle defining a volume and a discharge orifice in fluidcommunication with one another, the nozzle including an exhaust passagein fluid communication with the volume; a source of a pressurized gas inselective fluid communication with the volume of the nozzle; and a mediasupply in fluid communication with the volume of the nozzle such thatmetal from the media supply is movable into the volume, wherein theexhaust passage has an adjustable back pressure to control a pressureprofile in the volume of the nozzle as the pressurized gas moves throughthe volume to eject a liquid form of the metal from the dischargeorifice along a controlled three-dimensional pattern for fabrication ofa three-dimensional object.
 2. The system of claim 1, wherein theexhaust passage includes a hydraulic inductance, the hydraulicinductance having a dissipating resistance to flow in response to forceexerted, over a period of time, on the hydraulic inductance by ventingpressurized gas in the exhaust passage.
 3. The system of claim 2,wherein the hydraulic inductance includes a paddle wheel rotatable inresponse to force exerted on the paddle wheel by venting pressurized gasin the exhaust passage.
 4. The system of claim 2, a paddle wheelrotatable in response to force exerted on the paddle wheel by ventingpressurized gas in the exhaust passage.
 5. The system of claim 2,wherein a time-varying profile of the resistance of the hydraulicinductance is adjustable.
 6. The system of claim 1, wherein the exhaustpassage includes a variable hydraulic resistance.
 7. The system of claim6, wherein the variable hydraulic resistance includes a variable lengthof the exhaust passage.
 8. The system of claim 6, wherein the variablehydraulic resistance includes a flow restriction having a variable size.9. The system of claim 1, further comprising a valve in fluidcommunication with the source of the pressurized gas and the volume, thevalve actuatable to deliver pulses of the pressurized gas to the volume.10. A method of additive manufacturing, the method comprising: directinga metal into a volume defined by a nozzle, the volume in fluidcommunication with an exhaust passage defined by the nozzle; moving adischarge orifice and a build plate relative to one another along acontrolled three-dimensional pattern, the discharge orifice defined bythe nozzle and in fluid communication with the volume; delivering pulsesof pressurized gas into the volume of the nozzle; and adjusting a backpressure of the exhaust passage through which the pressurized gas isvented from the volume of the nozzle, wherein, in response to theadjustment of the back pressure, the pressurized gas in the volumeexerts a force on a liquid form of the metal in the nozzle to eject theliquid metal from the discharge orifice as the discharge orifice and thebuild plate are moved relative to one another along the controlledthree-dimensional pattern to form a three-dimensional object on thebuild plate.
 11. The method of claim 10, wherein adjusting the backpressure of the exhaust passage includes venting the pressurized gasthrough a hydraulic inductance having a dissipating resistance to flowin response to force exerted, over a period of time, on the hydraulicinductance by the venting pressurized gas in the exhaust passage. 12.The method of claim 11, wherein the dissipating resistance dissipates toa substantially constant hydraulic resistance over the period of time.13. The method of claim 12, wherein the period of time is less than aperiod of the pulses of pressurized gas delivered into the volume of thenozzle.
 14. The method of claim 11, wherein the hydraulic inductanceincludes a paddle wheel rotatable in response to force exerted on thepaddle wheel by the venting pressurized gas in the exhaust passage. 15.The method of claim 10, wherein adjusting the back pressure of theexhaust passage includes venting the pressurized gas through a variablehydraulic resistance and adjusting the variable hydraulic resistancebased at least in part on a position of the discharge orifice withrespect to the controlled three-dimensional pattern.
 16. The method ofclaim 15, wherein the variable hydraulic resistance includes a flowrestriction having a variable size and varying the variable hydraulicresistance includes changing the size of the flow restriction.
 17. Themethod of claim 15, wherein the variable hydraulic resistance includes avariable length of the exhaust passage and varying the variablehydraulic resistance includes changing the length of the exhaustpassage.
 18. The method of claim 10, wherein adjusting the back pressureof the exhaust passage is based on a volume of the liquid form of themetal in the volume of the nozzle.
 19. The method of claim 10, whereinthe exhaust passage is vented to at least one of atmospheric pressureand a vacuum.
 20. The method of claim 19, the metal is directed into thevolume through the exhaust passage.
 21. The method of claim 10, furthercomprising tuning the pulses of pressurized gas in a multiple of anatural harmonic of the volume of the nozzle.